1. Field of the Invention
The present invention relates to a liquid discharge head which is provided in an ink-jet recording apparatus which performs a recording operation by discharging ink or other liquids.
2. Description of the Related Art
An inkjet recording apparatus which records characters and images into a recording medium by discharging ink has a liquid discharge head (inkjet recording head) which discharges ink. The configuration and manufacturing method of a liquid discharge head which is composed of cylindrical ink discharge portions (piezoelectric elements) made of piezoelectric material and has a pressure chamber whose volume is able to be reduced by a deformation of the ink discharge portion due to voltage application are disclosed in Japanese Patent Application Laid-Open No. 2007-168319.
The liquid discharge head includes a unit stack (piezoelectric element substrate) and has a plurality of ink discharge portions each of which is formed in a square cylinder shape and has a passing hollow formed inside. More specifically, the ink discharge portion is composed of four wall portions constituting a pressure chamber which is formed by the aforementioned hollow and discharges ink. Upon supply of an electrical signal to the ink discharge portion, the four wall portions constituting the pressure chamber inflate into a barrel shape, thereby reducing the volume of the pressure chamber to discharge ink accumulated in the pressure chamber.
The pressure chambers are formed by the same number of grooves by stacking a plurality of piezoelectric material plates (piezoelectric plates), in which a plurality of grooves extending in the same direction is formed, with the grooves aligned in direction. Thereafter, the stacked piezoelectric material plates are cut in a direction orthogonal to the groove direction, by which a plate-like unit stack in which the pressure chambers are arranged in a matrix is obtained. Ink discharge portion separation grooves are formed so as to surround each of the pressure chambers arranged in a matrix of the unit stack, by which two or more cylindrical ink discharge portions separate from each other are formed. Thus, the unit stack has a matrix of high-density pressure chambers defined by the groove pitch of the piezoelectric material plate and the thickness of the piezoelectric material plate.
The unit stack having the ink discharge portions is assembled with an orifice plate (nozzle plate), a printed-wiring board, a rear throttle plate (supply passage plate), and a common liquid chamber (ink pool plate), by which a liquid discharge head is completed.
In the invention disclosed in Japanese Patent Application Laid-Open No. 2007-168319, each ink discharge portion is formed in a substantially independent square cylinder shape. Therefore, the wall portion is thin in thickness in the range of the outer peripheral surface of the ink discharge portion to the inner peripheral surface (the inner surface of the pressure chamber), which leads to low durability of the ink discharge portion. In the case of discharging high-viscosity ink for high-quality picture recording, it is necessary to increase the ink discharge force of the pressure chamber, which requires a longer pressure chamber. To make the pressure chamber longer, however, the ink discharge portion needs to be elongated, and the elongation of the thin wall portion of the square-cylinder-shaped ink discharge portion having the hollow further reduces the durability of the ink discharge portion. This might disable ink discharge due to breakage of the wall portion of the ink discharge portion which is caused by vibration generated when characters or images are recorded into a recording medium or the deflation of the ink discharge portion repeated to discharge the high-viscosity ink. Therefore, it is required to provide a durable ink discharge portion capable of discharging high-viscosity ink.
Meanwhile, in order to form the ink discharge portion into a square cylinder shape, it is necessary to form an ink discharge portion separation groove which forms a square cylinder shape around each of the pressure chambers arranged in a matrix in the unit stack. For high-resolution recording, it is desired to arrange the ink discharge portions which discharge ink densely as much as possible. In the invention disclosed in Japanese Patent Application Laid-Open No. 2007-168319, however, an ink discharge portion separation groove exists between ink discharge portions adjacent to each other and therefore the width of each ink discharge portion separation groove needs to be reduced to increase the density. The ink discharge portion separation groove is formed by a cutting process such as sandblasting or the like and therefore there is a limit on the reduction in the width of the ink discharge portion separation groove. This results in a large arrangement pitch of the cylindrical ink discharge portion, by which it is impossible to arrange the ink discharge portions densely in the unit stack.
Further, in the invention disclosed in Japanese Patent Application Laid-Open No. 2007-168319, common electrodes having the ground potential and individual electrodes independent of each other are wired on the same printed-circuit board. Therefore, it is required to wire the respective individual electrodes away from the respective common electrodes so as not to electrically come in contact with the common electrodes, which requires the common electrodes to be collectively arranged in one part. Accordingly, there is provided a common electrode post (a piezoelectric body for connecting the common electrodes) for electrically collecting the common electrodes together. The common electrode post is disposed by using a space of one line of the ink discharge portion on the unit stack. As a result, one line of the ink discharge portion needs to be eliminated in the arrangement, by which the ink discharge portions are not densely arranged on the unit stack. Therefore, it is required to provide a unit stack having ink discharge portions more densely arranged so as to achieve recording at higher resolution.